The present invention relates generally to metallic structures having protective coatings and methods for producing such structures. More particularly, the invention provides metallic components for incorporation in orthopedic prosthesis which include surfaces having integrally formed protective coatings that exhibit a high degree of hardness, wear and corrosion resistance.
Metallic structures are utilized in a variety of devices. For example, many prosthetic devices include metallic components. In particular, prosthetic joints, utilized in total joint arthroplasty (TJA) procedures to restore mobility in patients with reduced joint function, typically include two mating and articulating surfaces, one of which is formed of a metal alloy such as titanium-aluminum-vanadium or cobalt-chromium-molybdenum, and the other is formed and/or lined with a plastic component, such as ultrahigh molecular weight polyethylene (UHMWPE).
The recent trends in performing arthroplasty on younger and more active patients have increased the demand for enhanced prosthetic joint function and lifetime. The lifetime of total joint replacement components is typically limited either by gross failure of the materials of the articulating surfaces (primarily the UHMWPE component) or by biological reactions to debris generated from the wear of the articulating surfaces. UHMWPE wear particles have been implicated as a major contributing factor to bone resorption, joint loosening, and osteolysis, necessitating replacement of the prosthetic components. In addition, wear debris can result in the formation of scar tissue which, in turn, can lead to decreased joint mobility and pain. For example, wear of the UHMWPE acetabular component in artificial hips has been measured to be between 0.02 and 0.25 mm/year, with an average wear rate of about 0.07 mm/year.
A number of mechanisms can contribute to the rate of the wear of UHMWPE articulating surfaces. One such mechanism is abrasive wear which is caused primarily by surface asperities on a hard metallic or ceramic surface in contact with the UHMWPE articulating surface. Further, wear particles, such as metallic and ceramic particles, corrosion products, and bone fragments can migrate to the joint capsule and accumulate at bone prosthesis interface. These third body wear particles, produced primarily from components of bone cement used to secure the joints, produce a wear environment that facilitates roughening of the metallic surfaces.
One suggested approach for lowering the wear rate of UHMWPE components in such prosthetic devices is to coat the metallic mating surfaces with hard ceramics. However, such ceramic coatings have a number of drawbacks. For example, it is difficult to achieve adequate adhesion between the metal and the ceramic. Further, such ceramic coatings are brittle and can render manufacturing of the prosthetic devices which utilize them difficult and costly.
Thus, a need exists for protective coatings on metallic surfaces that can enhance the hardness, and the wear and corrosion resistance of such surfaces. Further, a need exists for metallic components in prosthetic devices which exhibit a high degree of wear and corrosion resistance. In addition, a need exists for methods of manufacturing such coatings which are easy to implement and are also cost effective.